1. Field of the Invention
The invention relates to a color cathode-ray tube (CRT) and, more particularly to a method of manufacturing a luminescent screen assembly for a color cathode-ray tube.
2. Description of the Background Art
A color cathode-ray tube (CRT) typically includes an electron gun, an aperture mask, and a screen. The aperture mask is interposed between the electron gun and the screen. The screen is located on an inner surface of a faceplate of the CRT. The aperture mask functions to direct electron beams generated in the electron gun toward appropriate color-emitting phosphors on the screen of the CRT.
The screen may be a luminescent screen. Luminescent screens typically comprise an array of three different color-emitting phosphors (e.g., green, blue, and red). Each color-emitting phosphor is separated one from the other by a matrix line. The matrix lines are typically formed of a light-absorbing black inert material.
Luminescent screens may be formed using an electrophotographic screening (EPS) process. In EPS processes, an organic photoconductive (OPC) layer is sprayed over an organic conductive (OC) layer, formed on an interior surface of a faceplate panel having matrix lines formed thereon. The three different color-emitting phosphors are than sequentially deposited on portions of the OPC layer. Each of the three different color-emitting phosphors is sequentially deposited by first uniformly charging the OPC layer and then selectively discharging portions thereof. Appropriate charged color-phosphors are then deposited on the discharged portions of the OPC layer.
However, after the first color-emitting phosphor lines are deposited on the OPC layer, the phosphor-deposited portions of the OPC layer have a higher electrostatic potential than the bare OPC portions. When the OPC is selectively charged and discharged to deposit the second color-emitting phosphor lines, this higher electrostatic potential causes the deposition of the second color phosphor lines to be misaligned with respect to the deposition of the first color-emitting phosphor lines.
Accordingly, a new method for forming the color phosphors on a luminescent screen is required.
The present invention relates to a method of manufacturing a luminescent screen assembly for a color cathode-ray tube (CRT). The luminescent screen assembly is formed on an inner surface of a faceplate panel of the CRT. The luminescent screen assembly includes an organic conductive (OC) layer over-coated with an organic photoconductive (OPC) layer. Three different color-emitting phosphors are sequentially deposited over portions of the OPC layer by uniformly charging and than selectively discharging desired areas thereof. Appropriate coloremitting phosphors are then deposited on the discharged areas. The first coloremitting phosphor lines are deposited on the OPC layer by charging and then selectively discharging the OPC layer using a symmetric exposure profile. Thereafter, the OPC layer is charged again and selectively discharged to deposit the second color-emitting phosphor lines using an asymmetric exposure profile. The asymmetric exposure profile is generated using two or more lighthouse exposures that are asymmetrically positioned relative to the midpoint location of the second coloremitting phosphor lines. The asymmetric exposure profile for the second color phosphor lines minimizes any misalignment of the second color-emitting phosphor lines with respect to the first color-emitting phosphor lines. Thereafter, the OPC layer is again charged and selectively discharged to deposit the third color phosphor lines using a symmetric exposure profile.